Why do we need signage up in the air that high? It doesn't ADD to the architecture... and it cheapens the building as it essentially becomes a huge billboard in the sky.
If a building is going to be associated with a brand or a company, they should be built as unique.
Does the Empire State Building have logos? The Willis Tower, the Burj Khalifa, the CN Tower, The original Twin Towers, the Petronas towers?
Do we want this kind of thing?
Not allowing signage up high can serve to INCREASE the architectural quality of a building as it has to stand out based on its own merits. Besides, businesses don't make business decisions on the ability to put a sign atop the building, there are lots of things that are taken into consideration.